Brush seal devices which have a brush portion made of multiple bristles are effective because the brush portion is deformed in accordance with movement of a rotational shaft and free end portions of tips of the bristles can follow a circumferential surface of the rotational shaft even if the rotational shaft is slightly moved in a radial direction.
However, when the bristles of a brush seal are pressed by movement of the rotational shaft, it is extremely difficult to control friction force applied thereto in an optimum state. This is because the friction force is affected by spring constant for elastic deformation of the bristles, complex friction force resulting from mounting structure of the bristles, and the like.
When the bristles do not properly follow the displacement of the rotational shaft, space occurs between the bristles and the rotational shaft. Then, this leads to leakage of process fluid or to an early wear of the free end portions of the bristles or a circumferential surface of the rotational shaft.
As a brush seal device to overcome such a problem, that is, as a brush seal device having a higher following ability and less wear, one having a floating-type brush seal body to enable a relatively large movement in the radial direction is lately used. Alternatively, a brush seal with a plate spring at an outer circumference, which can prevent eccentricity even if space occurs between a rotor and the brush seal due to wear thereof, is also known (for example, see Japanese Laid-Open Patent Publication No. 2011-169319 (Patent Document 1)).
However, for example, in a structure with a floating-type brush seal body or a structure with a plate spring at an outer circumference as shown in Japanese Laid-Open Patent Publication No. 2011-169319 (Patent Document 1), the outer circumference is not sufficiently sealed. Thus, a secondary seal surface is needed to prevent leakage from the outer circumference. However, in this structure, the outer circumferential side and a portion of the secondary seal are directly exposed to the outer circumferential leakage, which then increases the cost for sealing ability. In order to prevent the leakage of the secondary seal surface, a high-performance secondary seal is needed to be placed. Thus, in this respect, the cost is also increased. Further, the following ability for the rotational shaft is desired to be improved greatly.